The long-term goal of this project is to study in sheep: (1) the substrates and excretory products exchanged between maternal blood, placenta and fetal blood and (2) the factors that control this exchange. Fetal glucose and lactate metabolism will be studied by means of radiotracer techniques. The effects of chronic insulin and glucose infusions on fetal glucose uptake and utilization will be measured. A study of the regulation of uterine blood flow in early pregnancy will be initiated by measuring the flow response to the injection and continuous infusion of estrogens.